Titanosaurus

The holotype vertebrae were discovered during an exploration to Jabalpur in 1828 by Capt William Henry Sleeman of the East India Company army. He was one among many explorations for fossils initially carried out by army personnel, medical doctors and priests who chanced upon them just by being “fairly literate and mobile at the time”. He stumbled across the vertebrae on Bara Simla Hill near a British Army gun carriage workshop while searching for petrified wood. Sleeman, employed by the Bengal Army, regarded the bones as curiosities. He gave two vertebral pieces to surgeon G. G. Spilsbury, who had a practice in Japalpur and who also excavated a bone himself. Spilsbury sent the fossils in 1832 to the antiquarian James Prinsep in Calcutta, who realised that they were fossilised bones and then sent them back to Sleeman.[4] In 1862, Thomas Oldman, the first director of the newly established Geological Survey of India, transferred the vertebrae from Japalpur to Calcutta and added them to the collection of the Indian Museum. There, the bones were studied by the Survey's supervisor, Hugh Falconer, who concluded that they were reptilian bones.[5] After Falconer's death, in 1877, Richard Lydekker described the vertebrae as a new species of reptile known as Titanosaurus indicus.[1]

The known remains of T. indicus were generally considered to be lost and untraceable by the end of the twentieth century; in 2010 Matthew Carrano therefore established a cast based on illustrations Lydekker made in 1877, as a replacement plastotype, with the inventory number NHMUK 40867. However, that turned out to be a bit premature. In the early twenty-first century, Indian paleontologist Dhananjay Mohabey understood that such specimens were lost only because no serious inventory of the collections had been carried out for generations.[6] He therefore started the Study of Late Cretaceous Tetrapod fossils from Lameta Formation project with support from the University of Michigan, with one of the main goals of locating lost specimens.[6] In this context, he and Subhasis Sengupta recovered one of the holotype vertebra on 25 April 2012.[7] It turned out to be in a batch of fossils that had been left behind by Lydekker in 1878 that had been lost up until then, which is why no official inventory number of the GSI had been assigned to it.[8]

Part of the fossils that Lydekker assigned to the type specimen of T. indicus, that formed a series of syntypes, was a 1.5 metres (4.9 ft) long femur that had been excavated at the same location in 1871 or 1872 by Henry Benedict Medlicott - specimen GSI K22/754.[1] In 1933 this was reassigned by Charles Alfred Matley and Friedrich von Huene to Antarctosaurus septentrionalis,[9] which was moved to the new genus Jainosaurus in 1995.[10]

T. blanfordi holotype distal caudal vertebra (GSI 2195)

Between 1860 and 1870, geologist William Thomas Blanford had found two sauropod middle caudal vertebrae near Pisdura (one vertebra, GSI 2195, became the type specimen). In 1879, they were named by Lydekker as a second species of Titanosaurus, T. Blanfordi,[3] which according to current rules should be written as Titanosaurus blanfordi. Of the two fossils, making up specimen GSI IM K27 / 501, the second, smaller vertebra was split off by von Huene in 1929 and assigned to Titanosaurus araukanicus (now Laplatasaurus).[11][12] Upchurch & Wilson concluded in their 2003 revision that this assignment was unfounded, although there is indeed no evidence beyond their origin that the two vertebrae have anything to do with each other.[13] The large vertebra, strongly procoel, convex in front, is distinguished by a square cross-section, the lack of a trough on the underside and elongated proportions. These features are also found in other titanosaurs, although not found in India – the latter, however, was insufficient reason for Upchurch & Wilson not to speak of a nomen dubium. The holotype vertebrae of T. blanfordi were also missing for years and were rediscovered in 2012 by Dhananjay Mohabey and Subhasis Sengupta at the same location as the holotype of T. indicus.[8]

As the type genus of Titanosauria, Titanosaurus at times became a wastebasket taxon for a number of titanosaurs, including those not just from India but also southern Europe, Laos, and South America. Only two among these, however, are currently considered species of Titanosaurus: T. indicus and T. blandfordi, both of which are considered nomina dubia.

Other species formerly referred to this genus include:

• "Titanosaurus" rahioliensis - Described based on teeth, this species is now considered an indeterminate neosauropod as it shows similarities to Nigersaurus teeth[13]
• "Titanosaurus" colberti - This species was the most well-known species of Titanosaurus, but has been moved into its own genus, Isisaurus.[13][14]
• "Titanosaurus" australis - Known from relatively complete remains, but has been renamed Neuquensaurus.[13]
• "Titanosaurus" nanus - A small species found to be non diagnostic, and hence a nomen dubium.[13]
• "Titanosaurus" robustus - Now referred to Neuquensaurus.[13]
• "Titanosaurus" madagascariensis - nomen dubium; UCB 92305 apparently related to Vahiny, while UCM 92829 has been reassigned to Rapetosaurus.[13]
• "Titanosaurus" falloti - This large species, native to Laos, has disputed affinities. It has been considered synonymous with Tangvayosaurus and Huabeisaurus, but the remains are too fragmentary to be sure.[13][15][16]
• "Titanosaurus" valdensis - Referred to a new genus, Iuticosaurus, but still considered a nomen dubium.[13]
• "Titanosaurus" lydekkeri - Also referred to Iuticosaurus, but its relation to I. valdensis is uncertain.[13]
• "Titanosaurus" dacus - A dwarf titanosaur; now moved to the genus Magyarosaurus.[13]